Head blocks or head frames are mechanical devices having sheaves on an upper side and engagement devices, such as twist locks or connecting pins, on a lower side. The engagement devices are intended to come into contact with a spreader so as to couple the head frame and spreader. This is typically used for swapping spreaders for maintenance purposes. Other purposes include switching between a twin spreader arrangement to a single spreader arrangement such as for a system disclosed in WO2006/083230, WO2008/136766 and WO2008/136767, the contents of which are incorporated herein by reference. The pin or twist lock connections allow a spreader to be attached to the head frame or removed from it for maintenance or other purposes.
Unlike the twist lock arrangements used for a spreader to engage a container, the twist lock and pin connection of a head frame are normally engaged manually. This manual engagement, as compared to a powered arrangement, is a reflection of the frequency with which a spreader is removed from a head frame. Whilst a spreader will engage many containers in a single day, maintenance may occur only once every several months. Consequently, there is no pressing need to include a powered system in order to engage and disengage the twist locks or other engagement devices coupling a head frame to a spreader.
In any event, even if the engagement device was automated at some point, it would be necessary for a manual operation as the electrical connection between the head frame and the spreader also needs to be disconnected and reconnected on engagement which again must be manually perform.